An optical transmission circuit apparatus that enables high-speed signal transmission between boards is disclosed in Japanese Patent Application Laid-Open No. 2006-067360. This apparatus comprises a bottom plate in which the boards are arrayed, and an optical transmission circuit that connects these boards is provided in the bottom plate. The optical transmission circuit comprises a tape-like optical fiber bundle, an optical divergence unit, and an optical connection unit. The optical fiber bundle is formed by arraying optical fibers in parallel. The optical divergence unit is connected with the optical fiber bundle and changes the direction of light that propagates in the optical fibers. The optical connection unit is connected with the optical divergence unit and a photoelectricity conversion circuit mounted on the board. The optical transmission circuit propagates an optical signal in the width direction of the bottom plate and change an optical path upward by the optical divergence unit, thereby propagating the optical signal to the photoelectricity conversion circuit.